20668639 has 2 divisors, whose sum is σ = 20668640. Its totient is φ = 20668638.

The previous prime is 20668631. The next prime is 20668643. The reversal of 20668639 is 93686602.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20668639 - 2³ = 20668631 is a prime.

It is a super-2 number, since 2×20668639² = 854385276224642, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20668631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10334319 + 10334320.

It is an arithmetic number, because the mean of its divisors is an integer number (10334320).

Almost surely, 2^20668639 is an apocalyptic number.

20668639 is a deficient number, since it is larger than the sum of its proper divisors (1).

20668639 is an equidigital number, since it uses as much as digits as its factorization.

20668639 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 93312, while the sum is 40.

The square root of 20668639 is about 4546.2774882314. The cubic root of 20668639 is about 274.4336067022.

The spelling of 20668639 in words is "twenty million, six hundred sixty-eight thousand, six hundred thirty-nine".